There are many cosmetics containing powders, such as cosmetics for foundation, cosmetics for make-up (e.g., eye shadow) and cosmetics for the body (e.g., body powder, baby powder). However, it has been found impossible that all of the performances such as smoothness, adhesion, etc., required for cosmetics of good quality are fully satisfied by cosmetic powders conventionally used, for example, inorganic extender pigments such as talc; inorganic coloring materials such as zinc oxide; organic coloring materials such as organic tar dyes; composite pigments such as micaceous titanium; and powders having surfaces treated with conventional coating agents such as silicone.
Accordingly, metallic soaps are often blended with cosmetics to impart smoothness, adhesion, etc., thereto. However, it is not considered that satisfactory performances are fully imparted to such cosmetics by the metallic soaps with respect to smoothness, adhesion, etc.
Spherical polymers such as nylon powder and styrene polymers are also used as cosmetic materials for imparting smoothness, adhesion, etc. However, they have disadvantages in that they are bulky to the feel and adhesion is poor, so that flexibility and wetness can not be imparted to the cosmetics. Further, they have disadvantages in that the adhesion of the cosmetics to the skin is deteriorated and press-moldability is lowered.
The present inventors had previously found that metal salts of monoalkylphosphoric acids have properties such as smoothness, adhesion, etc., suitable for use as cosmetic powders. As a result, a patent application relating to a cosmetic containing the same was filed (see JP-A-1-125314 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")). Further, there was filed a patent application relating to a process for economically preparing metal salts of monoalkylphosphoric acids having performances suitable for use as cosmetic powder by using mixed solvents of water and water-soluble organic solvents as solvents for reaction (see, JP-A-61-229889 (corresponding to U.S. Pat. No. 4,804,533)). The present inventors had already found that among the metal salts of monoalkylphosphoric acids, zinc monoalkylphosphate particles have particularly excellent performance as a lubricant and as a cosmetic powder. However, it was found that after the completion of the formation of zinc salt, the reaction system is strongly acidified (in many cases, PH&lt;2) in the conventional process, and zinc monoalkylphosphates are produced in the crystalline form of needle crYstals, or a mixture of platy (including scaly) and needle crystals, or in an amorphous form, under the above acidified conditions. There was much difficulty in preparing zinc monoalkylphosphates mainly composed of platy crystals (including scaly crystal). When such mixtures of variOus crystal forms are used, unevenness in coating is caused, a whitish tone is left behind, and satisfactory performances as a lubricant and as a cosmetic powder can not be obtained. Further, the size of these particles is often non-uniform and it is necessary to provide a classification step and a crushing step when they are used as a lubricant.
Accordingly, it has been highly demanded to develop metal salts of monoalkylphosphoric acids which are excellent in safety and have excellent performances such as smoothness, transparent appearance, adhesion, water repellency, etc. as a lubricant and as a cosmetic powder.